FFF,
The argument about examiners use the CRP5 so everyone must use them is erroneous.
My experience has been that the spread of answers using CRPs is greater than the spread of answers using Jep. CR types (CR5, CR2 & CR1). At all times on the courses I've attended all Jep CR answers provided by the 6 or 8 of us using them were in a tight cluster well within the CRP5 spread given by the rest of the class.
If anything that's a justification for changing in itself.
Exam questions must allow for accuracy limits of the tools used to derive the answers. As long as answers provided by a tool are constrained within deviation limits of equivalent tools used as a benchmark then any tolerance (or lack thereof...
) of exam question options is irrelevant.
Your argument about UK instructor familiarity has some basis however it is only the wind side that differs substantially. Not so substantially that it can't be self taught from the manual that comes with it (I, and many others I know, did).
The calculator side works the same for most calculations except that there are additional scales that allows one to skip some steps that must be done with the CRP type for Mach No. calculations - again, all explained quite clearly in the manual.
There IS a matter of comfort & familiarity but this cuts both ways. I feel the portability & convenience, ease of use & speed of a CR type vastly outweighs a period of adjustment.
I used an E6B type slide type (Still have it - a Kane etched aluminium one. No longer available) for my PPL, night & CPL training and then switched to a CR5 (the smallest & therefore the least accurate) for IR, Oz ATPL, FAA ATP & UK ATPL.
In no case was the CR a detriment and in some exam problems it was an advantage.